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S A Egorov

Publications and source records attributed to S A Egorov.

12 recordsLinked to original sources
PubMed2007

Steric stabilization of spherical colloidal particles: Implicit and explicit solvent.

We present the results of Monte Carlo simulations and density functional theory treatment of interactions between spherical colloidal brushes both in implicit (good) solvent and in an explicit polymeric solution. Overall, theory is seen to be in good agreement with simulations. We find that interactions between hard-sphere particles grafted with hard-sphere chains are always repulsive in implicit solvent. The range and steepness of the repulsive interaction is sensitive to the grafting density and the length of the grafted chains. When the brushes are immersed in an explicit solvent of hard-sphere chains, a weak mid-range attraction arises, provided the length of the free chains exceeds that of the grafted chains.

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PubMed2005

Interactions between nanocolloidal particles in polymer solutions: effect of attractive interactions.

We present a density-functional theory study of nanoparticle interactions in a concentrated polymer solution. The polymers are modeled as freely jointed tangent chains; all nonbonded interactions between polymer segments and nanoparticles are described by Lennard-Jones potentials. We test several recently proposed methods of treating attractive interactions within the density-functional theory framework by comparing theoretical results with recent simulation data. We find that the simple van der Waals approach provides the most accurate results for the polymer-mediated potential of mean force between two dilute nanoparticles. We employ this approach to study nanoparticle interactions as a function of nanoparticle-segment interaction strength and polymer solution density and temperature.

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PubMed2005

Interactions between nanoparticles in supercritical fluids: from repulsion to attraction.

We present a density functional theory study of interactions between sterically stabilized spherical nanoparticles in a supercritical solvent. The theory is used to analyze the effect of particle size, solvent density, and solvent-ligand interaction strength on the potential of mean force between the particles. Experimentally observed size-selective precipitation of nanoparticles is rationalized in terms of the behavior of the density profiles of stabilizing ligands as a function of particle size and solvent thermodynamic conditions. The theory yields the same general trends as observed in experiments, namely, an increased stability of nanoparticle dispersions at higher solvent densities and for smaller particle sizes.

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PubMed2005

A mode-coupling theory of vibrational line broadening in near-critical fluids.

We present a fully microscopic mode-coupling theory of near-critical line broadening. All the structural and dynamical input required by the theory is calculated directly from intermolecular potentials. We compute vibrational frequency time-correlation functions and line shapes as the critical point is approached along both the critical isochore and the liquid-gas coexistence curve. Theory is shown to be in good agreement with simulation.

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PubMed2004

Polar solvation dynamics in supercritical fluids: a mode-coupling treatment.

A mode-coupling treatment of polar solvation dynamics in supercritical fluids is presented. The equilibrium solvation time correlation function for the solute fluctuating transition frequency is obtained from the mode-coupling theory method and from molecular-dynamics simulations. The theory is shown to be in good agreement with the simulation. The solvation time correlation function exhibits three distinct time scales, with rapid initial decay, followed by a recurrence at intermediate times, and a slowly decaying long-time tail. Our theoretical analysis shows that the short-time decay arises from the coupling of the solute energy gap to the solvent polarization modes, the recurrence at intermediate times is due to the energy modes, while the slow long-time decay reflects the coupling to the number density modes.

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PubMed2004

Solvation dynamics in supercritical fluids: equilibrium versus nonequilibrium solvent response functions.

We present a theoretical study of solvation dynamics in supercritical fluids. Molecular dynamics simulations show a significant difference between equilibrium and nonequilibrium solvent response functions, especially pronounced at medium and low solvent densities. We propose an analytical theory for the nonequilibrium solvation function based on the generalized nonlinear Smoluchowski-Vlasov equation. The theory is shown to be in good agreement with simulation, providing an accurate description of the nonequilibrium time-dependent solvent density profile around the solute over a wide range of supercritical solvent densities. The nonequilibrium solvent response function is shown to reflect gradual solvent clustering around the excited solute.

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PubMed2004

A simple theory of the interaction between polymer brushes immersed in a supercritical fluid.

We use a simple two-order parameter model to describe the interaction between the brushes of polymers terminally attached to flat surfaces immersed in a supercritical solvent. Our approach makes it possible to take into account the high compressibility of the supercritical solvent, which proves to give a significant contribution to the disjoining force acting between polymer brushes. Our theory explains why the interaction between brushes can change from repulsive to attractive with decreasing solvent density. This theoretical finding is verified by making a comparison with recent computer simulations. A reasonably good agreement between the results of the present theory and the simulations is found.

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PubMed2004

Effect of repulsive and attractive interactions on depletion forces in colloidal suspensions: a density functional theory treatment.

The author employs density functional theory to study colloidal interactions in solution. Hardcore Yukawa potentials with soft tails, either repulsive or attractive, are used to model colloid-solvent and solvent-solvent interactions. We analyze the effect of these interactions on the solvent-mediated potential of mean force between two colloids in solution. Overall, theory is shown to be in good agreement with recent simulation data. We use the theory to study the density dependence of the colloid-colloid second virial coefficient.

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PubMed2004

Interactions between colloidal particles in polymer solutions: A density functional theory study.

We present a density functional theory study of colloidal interactions in a concentrated polymer solution. The colloids are modeled as hard spheres and polymers are modeled as freely jointed tangent hard sphere chains. Our theoretical results for the polymer-mediated mean force between two dilute colloids are compared with recent simulation data for this model. Theory is shown to be in good agreement with simulation. We compute the colloid-colloid potential of mean force and the second virial coefficient, and analyze the behavior of these quantities as a function of the polymer solution density, the polymer chain length, and the colloid/polymer bead size ratio.

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PubMed2004

Ion solvation dynamics in supercritical fluids.

We present a theoretical study of ion solvation dynamics in a supercritical solvent. Molecular dynamics simulations show a significant difference between equilibrium and nonequilibrium solvent response functions, especially pronounced at medium and low solvent densities. We propose a simple analytical theory for the nonequilibrium solvation function based on the generalized nonlinear Smoluchowski-Vlasov equation. The theory is shown to be in excellent agreement with simulation over a wide range of supercritical solvent densities.

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